In order to have better power efficiency, the conventional DC-DC voltage regulator is controlled to provide an output voltage with one or more phases according to a loading. In detail, when the DC-DC voltage regulator provides the output voltage to a light load (i.e. less load current), the DC-DC voltage regulator may provide the output voltage with a single phase; on the other hand, when the DC-DC voltage regulator provides the output voltage to a heavy load (i.e. large load current), the DC-DC voltage regulator may provide the output voltage with two or more phases. However, when the load current decreases and the DC-DC voltage regulator switches from a dual phase mode to a single phase mode, an overshoot issue may occur on the load current, and the DC-DC voltage regulator may misunderstand that load becomes heavy, thereby the DC-DC voltage regulator immediately switches back to the dual phase mode. In light of above, a toggle between the dual phase mode and the single phase mode will always occur, and the power efficiency may be worsened.